1. Field of the Invention
This invention relates to improvements in the dissipation of energy due to seismic and other forces and, more particularly, to an improved energy absorbing apparatus which can be coupled to piping system and other structural elements where displacements due to such forces are to be controlled.
2. Description of the Prior Art
In nuclear and other types of power plants, piping systems are required to carry fluids of different types, such as high pressure steam, waste liquids and the like. It is extremely important that such piping systems remain intact and not be damaged in any way during the time when external forces are exerted thereon. Thus, the need to support the piping in such a way to provide direct support and energy absorption due to displacements of such a piping system is clearly obvious, and many attempts have been made in the past to provide support or energy dissipation devices for use in overcoming the problems which could arise if such piping systems were to be displaced beyond an acceptable limit.
Typically, there are two categories of loading of piping systems of the type described. The first of these categories is associated with static loading, such as those forces applied to a piping system due to thermal expansion. In such a case, supports must be designed to be sufficiently flexible so that pipe expansion will not be restricted so as to cause harmful pipe stresses. The second category is dynamic loading, such as applied forces due to seismic events. In this case, supports must be rigid enough to reduce displacements, accelerations and other piping dynamic responses. To satisfy both of the foregoing problems, it is necessary to provide support or energy absorbing means which is dependent upon the system frequency.
In conventional plant designs, the most frequently used device is a shock arrestor or snubber. Such a device introduces very low resistance at low velocity or acceleration but locks effectively whenever the piping system is vibrating at a higher frequency.
Conventional snubbers, however, do have some severe drawbacks. First of all, they are expensive, require maintenance, and are difficult to install or maintain in a complex piping system. Worst of all, at times snubbers lock instantaneously when the need arises and occasionally they may malfunction and inadvertently lock up when no such need exists. These drawbacks reduce the overall reliability of the installations on which snubbers are used. Even if these drawbacks are overcome, conventional snubbers still present problems in design and operating procedures. Since an elastically analyzed piping system where snubbers are used does not effectively dissipate energy, interaction between the piping system and the supporting structure using conventional snubbers can be so significant that both the piping system and the supporting structure cannot be designed independently of each other.
Other attempts have been made to provide improved energy absorbing devices which are adapted to be coupled to piping systems or the like. Certain of these devices have been disclosed in the following reports published by the College of Engineering University of California, Berkeley, Calif.:
1. Report No. UCB/EERC-80/33, September, 1980, entitled "Shaking Table Tests of Piping Systems with Energy Absorbing Restrainers" by S. F. Steimer and W. G. Godden. PA0 2. Report No. UCB/EERC-81/09, July, 1981, entitled "Experimental Behavior of a Spatial Piping System with Steel Energy Absorbers Subjected to a Simulated Differential Seismic Input", by S. F. Steimer, W. G. Godden and J. M. Kelly. PA0 3. Report No. UCB/EERC-82/03, May 1982, entitled "Behavior of a Piping System Under Seismic Excitation", by S. Schneider, H. M. Lee and W. G. Godden.
In the first of these reports, a single energy absorbing device is disclosed for use as the sole energy absorbing means at a particular location along the length of a pipeline. The device has a pair of opposed ends and a pair of side edges extending from one end and converging to the other end, whereby the other end has a narrowed configuration with respect to the one end. In the other two reports, a single energy absorbing device of a bow tie or X-shaped configuration is provided for a particular pipeline location for controlling the displacement of a piping system and thereby absorb the energy due to the moving pipeline. The device has a central narrow part and relatively wide outer end.
Generally, there are a number of problems associated with the use of devices of the type disclosed in the above reports. For instance, to keep the ends always parallel to each other, the way in which such a device is coupled to a piping system disallows the pipe to displace in a transverse direction or to rotate in any direction where such movements are desired.
Because of the foregoing drawbacks, a need has arisen for an improved apparatus for absorbing energy at each of a plurality of locations along a moveable piping system or other structural elements whose displacement is to be controlled to prevent structural damage thereto. The present invention satisfies the aforesaid need as hereinafter described.